Polyvinyl alcohol gel support pad

ABSTRACT

A polyvinyl alcohol gel pad. The gel pad has properties which make it useful as a support pad in the prevention and treatment of decubitus ulcers (also known as pressure sores) and for other purposes. The polyvinyl alcohol gel is made by cross-linking high molecular weight polyvinyl alcohol using a cross-linking agent, such as formaldehyde, in the presence of an acid catalyst, such as hydrochloric acid, and by incorporating at least one internal plasticizer, such as propylene glycol, in the gel. The support pad is completed by putting a thin-film envelope around the gel.

United States Patent Graves et al.

[ 1 Sept. 12, 1972 3,308,491 3/1967 Spence ..5/348 3,518,242 6/1970Chrisp.; ..260/91.3

Primary ExaminerBobby R. Gay

Assistant Examiner-Andrew M. Calvert Att0rney-Charles K. Wright, J r.,William G. Gapcynski and Lawrence A. Neureither [57] ABSTRACT Apolyvinyl alcohol gel pad. The gel pad has properties which make ituseful as a support pad in the prevention and treatment of decubitusulcers (also known as pressure sores) and for other purposes. Thepolyvinyl alcohol gelis made by cross-linking high molecular weightpolyvinyl alcohol using a cross-linking agent, such as formaldehyde, inthe presence of an acid catalyst, such as hydrochloric acid, and byincorporating at least one internal plasticizer, such as propyleneglycol, in the gel. The support pad is completed by putting a thin-filmenvelope around the gel.

4 Claims, 3 Drawing Figures DISPLAOEMENT- INCHES PAIENTEIJSEP I2 I972FIG.I

FIG.2

o 5 STRESS -STRAIN BEHAVIOR UNDER RAPID LOADING I I I I I I l A ,4 (D r"u f I I O o 0.5 -"Q -O E A a" I y In I 2 l g 0.2 f l O n. I A Q O o O/I,

0 PRIOR ART ORGANOSILOXANE GEL PAD A POLYVINYL ALCOHOL GEL SUPPORT PAD OO l l l I I I I I00 zoo :00 400 500 e00 100 800 LOAD- enms/ mcnssVISCOUS CREEP AND ELASTICITY OF GEL PADS I l I I l I I (LOADS GIVEN INcams/mau "nus zERo: 1.0m DECREASE!) FROM 758 T0 as POINT A: LOADINCREASED FROM 38 TO 519 W POINT a: LOAD DEGREASED FROM 319 To a FIG.3

A A B A l N 'ro answer-15s AT I046 MINUTES a PRIOR ART onsnuosmoxme GELPAD A POLYVINYL ALCOHOL GEL SUPPORT PAD I I l l I I 0 I00 200 300TIME-MINUTES INVENTORS DAVID J. GRAVES CHARLES R. RITCHEY A T TORNE)BACKGROUND OF THE INVENTION 1. Field of thelnvention This inventionrelates to the field of support padsfor bedridden patients. Moreparticularly, this invention relates to a polyvinyl alcohol gel supportpad useful for preventing and treating decubitus ulcers.

2. Description of the Prior Art The problem of preventing and treatingdecubitus ulcers has long vexed the medical art. The average cost of asingle decubitus ulcer (pressure sore) in terms of prolongedhospitalization, medical and nursing care, has been estimated at $2,000to $10,000. See W. Spence, Clinical Medicine, Nov. 1967, p. 25.Decubitus ulcers are a frequent complication in the case of burnpatients where the ulcerations delay final recovery. They areparticularly prevalent in tall, thin patients at pressure points such asthe heel, base of the spine, and elbow.

The prior art reveals several methods designed to ameliorate theproblem. One of the early devices employed was a water bed patented byC. Ewald on Jan. 16, I934 (U.S. Pat. No. 1,943,888). More recently therehave been polyurethane foam pads (U.S. Pat. No. 3,451,071), gas-filledcushions (U.S. Pat. No. 3,340,551), and combinations of elastomericpads, liquid-filled bladders, and air bladders (U.S. Pat. No.3,456,270).

More directly related to the present invention is the prior art seen inU.S. Pat. No. 3,308,491 issued March 14, I967 to W. Spence for CushionStructure. The

same prior art cushion structure is described and its method of use isexplained in Spence, Clinical Medicine, November I967, pp. -30. Dr.Spences cushion structure is presently in commercial use and those inthe art are familiar with it. Dr. Spences cushion structure is composedof a resiliently flexible and semisolid core and wall means forprotecting the core from external contamination. The core is describedas made of an organosiloxane gel, substantially of the type disclosedand described in U.S. Pat. No. 3,020,260, issued Feb. 6, 1962, to M.Nelson, for organosiloxane Potting Compound. The primary disadvantage ofthe organosiloxane gel is its very high cost, which is discussed by Dr.Spence in Clinical Medicine, November I967, at p. 27 and p. 30.

SUMMARY OF THE INVENTION A polyvinyl alcohol gel support pad comprisinga polyvinyl alcohol geland a thin-film envelope inclosing the gel. Morespecifically, the polyvinyl alcohol gel is a cross-linked irreversiblegel containing at least one inexchanging polyol molecules for the watermolecules entrapped in the gel. The gel is enclosed in athin-filmenvelope of a strong, flexible, elastic, and tear-resistant polymericmaterial. The polyvinyl alcohol gel support pad is useful in the art ofpreventing and treating decubitus ulcers and it is an improvement overthe prior art in this field of use because the polyvinyl alcohol gelexhibits the property of viscous creep which permits the gel to conformwith the body contours in contact with the pad.

Accordingly, it is an object of this invention to provide a support padfor the human body in which the support pressure is uniformlydistributed over a larger area so that pressure necrosis, decubitusulcers, and skin breakdown is largely eliminated.

A further object of this invention is to provide a support pad which iseasy to handle and maintain, which has long shelf life and which isnontoxic.

A further object of this invention is to provide a support pad composedof a gel which is easy to prepare from readily available commercialchemicals and which is, above-all, relatively inexpensive in total costas compared to prior art devices.

Other objects and purposes of this invention will be apparent from thefollowing description and the accompanying drawings.

BRIEF DESCRIPTION OF TI-IEDRAWINGS FIG. 1 is a vertical cross-sectionalview through a polyvinyl alcohol gel support pad.

FIG. 2 is a graph of test data comparing the stressstrain behavior underrapid loading of a prior art organosiloxane gel pad and the polyvinylalcohol gel support pad.

FIG. 3 is a graph of test datacomparingthe viscous creep and elasticityof a prior art organosiloxane gel pad and the polyvinyl alcohol gelsupport pad.

DESCRIPTION OF PREFERRED EMBODIMENTS The polyvinyl alcohol gel supportpad which is the finished product comprises two components shown incross-section in FIG. 1. The'pad 10 comprises a gel core 11 and athin-film envelope l2 inclosing the gel. The polyvinyl alcohol gel 11 isinelosed in the envelope 12 after the gel has been prepared and theenvelope is sealed in a conventional manner to make a finished pad.

EXAMPLE OF PREPARATION OF GEL The basic starting materials for thepolyvinyl alcohol gel are: (I) an aqueous solution of a high molecularweight polyvinyl alcohol; (2) formaldehyde solution; and (3)concentrated I-ICI.

The polyvinyl alcohol is inexpensive and commercially available in bulkquantities as a powder. A high molecular weight polyvinyl alcohol ispreferred. Du Pont Elvanol grade number 72-60 has been foundsatisfactory. This grade of high molecular weight polyvinyl alcohol hasthe following characteristics:

a. Viscosity in cp. of a 4 percent solids aqueous solution at 20 C.,determined by Hoeppler falling ball method: -65

b. Percent hydrolysis (mole percent hydrolysis of acetate groups, drybasis): 99.0 99.8

c. pH: 5.0-7.0

d. Volatiles, percent max.: 5 e. Ash, percent max. (dry basis,calculated as Na O): 1.0

f. Mean Molecular Weight: approximately 180,000.

The polyvinyl alcohol gel may be prepared in the following manner: 750grams of an aqueous percent solution of high molecular weight polyvinylalcohol is stirred together with 240 grams of a U.S.P. solution offormaldehyde (37 percent formaldehyde) used as a cross-linking agent and3 ml. of concentrated hydrochloric acid used as a catalyst. Othercommercially available cross-linking agents may be used in lieu of theformaldehyde and other acid catalysts may be used in lieu of HCl. Thisquantity of starting materials is sufficient to prepare a circular padseven inches in diameter, approximately three inches in thickness.

After thorough mixing, the viscous solution is placed in a container ormold of any desired shape, such as circular or square. The solution isthen heated at approximately 77 C. at atmospheric pressure for 2 2 m 3hours. The resulting polyvinyl alcohol gel is then removed from the moldand soaked in water for 3 days in order to rid the gel of any excessunreacted formaldehyde. Any formaldehyde which remains in the gelfollowing this soaking may be neutralized by soaking the gel in asolution prepared from 28 grams of urea in two pints of water for 3days, changing the urea solution daily.

It should be noted that the term gel is used in a special sense in thatthe gel which results from this synthetic process is like a single giantmolecule because the cross-linking process causes strong chemical bondsto form between the polyvinyl alcohol polymer chains. The resulting gelcannot be broken down by heat or physical manipulation short ofdestroying the gel completely. The gel is an aqueous polyvinyl alcoholgel because it is believed to contain water molecules trapped within thepolyvinyl alcohol structure. The entrapped water molecules appear to actas an internal plasticizer. But the gel is not like the gel of gelatinfood desserts where the physical structure is set up by weakintermolecular bonds after dispersal of the molecules with the aid ofheat and vigorous agitation. The gel of a gelatin dessert may be thoughtof as a reversible gel whereas the gel in the present polyvinyl alcoholgel is formed by an irreversible chemical reaction. It should also benoted that the present polyvinyl alcohol gel is different from the hardpolyvinyl alcohol plastic described in US. Pat. No. 2,083,628, issuedJune 15, 1937, to G. Zelger for Method of Making Vinyl DerivativeArticles.

A further step in the synthetic process is considered essential. It hasbeen found that the water trapped within the polyvinyl alcohol gel willslowly evaporate, even through a polyurethane envelope. When the waterevaporates, the gel becomes hard and useless. Therefore, an improved gelmay be made by partially or completely exchanging the water in the gelwith a nonvolatile nontoxic liquid such as propylene glycol. Thisexchange may be accomplished by soaking the aqueous gel in propyleneglycol before sealing the gel in the envelope 12. The step ofneutralizing unreacted formaldehyde and the step of exchanging theliquid trapped in the gel may be combined in one step by soaking theaqueous gel in two pints of propylene glycol containing 28 grams of ureafor three days, changing the solution each day. With propylene glycol inthe gel, the pad has an almost unlimited shelf and use life. It isthought that the water molecules and the propylene glycol molecules actas internal plasticizers in the polymer structure.

Propylene glycol cannot be combined with the polyvinyl alcoholinitially. Propylene glycol and urea are used in the foregoing examplebecause they are relatively innocuous physiologically. Other polyolswould function in place of propylene glycol, but propylene glycol ispreferred for its nontoxic character.

The polyvinyl alcohol gel made by the above procedure is essentiallycolorless. If it is desired to make a colored gel, a small amount offood coloring (F D and C dyes) may be added to the original startingsolution to give the gel a pleasant color.

EXAMPLE OF PREPARATION OF PAD I Once the polyvinyl alcohol gel has beenprepared, the final step in preparing the finished pad is to enclose thegel in a thin-film envelope 12 which is used to prevent contamination ofthe gel. For example, the gel may be enclosed in a heat-sealed envelope12 made of 0.002 gauge (2 mil thickness) polyurethane film such as typeTF 1 10 made by B. F. Goodrich Company. The envelope material must bestrong, flexible, elastic, and tear-resistant.

HOW TO USE THE PAD In actual use, the pad is placed under the patientspressure points where decubitus ulcers are likely to occur. Decubitusulcers are defined as an ulceration caused by prolonged pressure in apatient confined to bed for a long period of time. Ulceration is theloss of substance on a cutaneous or mucous surface, causing gradualdisintegration and necrosis of the tissue. See Dorlands IllustratedMedical Dictionary, 23rd edition 7). For purposes of this invention, theterm decubitus ulcer is broad enough to include any disintegration andbreakdown of the skin and tissue caused by prolonged pressure in apatient confined to a bed for a long period of time and we define theterm to specifically include the breakdown of skin and tissue after skingrafting in bedridden burn patients.

The polyvinyl alcohol gel conforms itself to the contour of the engagedsurface on the supported body so that the support pressure is uniformlydistributed over the entire area of engagement. In effect, the gel ofcross-linked polyvinyl alcohol distributes the weight over a greatersurface area and thus reduces the pressure per unit area. This pressuredistribution is useful in the prevention and treatment of decubitusulcers.

A comparison of the properties of the polyvinyl alcohol gel pad with theorganosiloxane gel pad of the prior art appears in FIG. 2 and FIG. 3.The tests in each case used a cylindrical penetrator withcross-sectional loads, the polyvinyl alcohol gel support pad has thedesirable characteristic of being softer or exhibiting greaterdisplacement than the prior art organosiloxane gel pad.

FIG. 3 shows that the viscous creep and elasticity behavior is not thesame in the two pads. As seen in FIG. 3, the polyvinyl alcohol gelsupport pad exhibits more viscous creep and its elastic reboundcharacteristic is slower than in the organosiloxane gel pad. Thesecharacteristics of the polyvinyl alcohol gel pad are regarded as animprovement over the prior art organosiloxane gel pad since thepolyvinyl alcohol gel support pad conforms atleast partially to bodycontours. Thus, if the polyvinyl alcohol gel pad is placed on a ribbedsurface for several hours, it will acquire a ribbed surfaceconformation. If removed from the ribbed surface, it will recover tosubstantially its original shape in several hours. The organosiloxanegel pad doesn't exhibit this behavior as may be seen by the data in FIG.3. The organosiloxane gel pad exhibits almost complete elasticity andalmost instantaneous recovery (rebound). A combination of viscosity andelasticity as exhibited by the polyvinyl alcohol gel support pad isbelieved to be an advantage since it permits the gel to conform to bodycontours.

Another physical property of interest is tensile strength. The ultimatetensile strength of the polyvinyl alcohol gel is 2.61 pounds per squareinch at an ultimate elongation of 450 percent. The ultimate tensilestrength of the organosiloxane gel is 0.71 pounds per square inch at anultimate elongation of 175 percent.

RESULTS The polyvinyl alcohol gel support pad has been successfullytested at Brooke General Hospital, Fort Sam Houston, Tex. Overone-hundred patients have been successfully treated with the pads. Thepads were used in providing nursing care for patients with extensiveburns, and they were very useful in preventing the breakdown of skinover pressure areas, as for example, when thin and debilitatedindividuals must necessarily remain in one position for prolongedperiods of time when skin grafting procedures are carried out. Inaddition to preventing skin damage, the pads also provided increasedpatient comfort.

OTHER USES In addition to preventing and treating decubitus ulcers inbedridden patients, other practical applications are obvious. Thepolyvinyl alcohol gel support pad may be used in any situation where theshock absorbing propeities of the gel are desired. In particular, theaircraft industry has unsuccessfully tried to develop a cushion toprevent coccyx fractures in aircraft pilots during high speed seatejections. The polyvinyl alcohol gel support pad answers this need at areasonable cost.

I claim:

1. A support pad comprising:

a. a polyvinyl alcohol gel, wherein said gel is a crosslinkedirreversible gel containing at least one internal plasticizer comprisinga polyol compound and said gel exhibits the physical propertyof a slightamount of viscous creep when placed under a load and the physicalproperty of slowly returning to its original conformation when said loadis removed,

b. iqin-film envelope inclosing said gel.

2. The support pad as defined in claim 1 wherein the thin-film envelopeis a strong, flexible, elastic and tearresistant polymeric material.

3. The support pad as defined in claim 2 wherein the polymeric materialis polyurethane.

4. In the art of preventing and treating decubitus ulcers in which it isknown to use an organosiloxane gel pad, the improvement comprising usinga polyvinyl alcohol gel support pad wherein said pad comprises:

a. a polyvinyl alcohol gel, wherein said gel is a crosslinkedirreversible gel containing at least one internal plasticizer comprisinga polyol compound and said gel exhibits the physical property of aslight amount of viscous creep and thereby conforms to body contours incontact with said pad; and

b. a thin-film envelope inclosing said gel.

2. The support pad as defined in claim 1 wherein the thin-film envelopeis a strong, flexible, elastic and tear-resistant polymeric material. 3.The support pad as defined in claim 2 wherein the polymeric material ispolyurethane.
 4. In the art of preventing and treating decubitus ulcersin which it is known to use an organosiloxane gel pad, the improvementcomprising using a polyvinyl alcohol gel support pad wherein said padcomprises: a. a polyvinyl alcohol gel, wherein said gel is across-linked irreversible gel containing at least one internalplasticizer comprising a polyol compound and said gel exhibits thephysical property of a slight amount of viscous creep and therebyconforms to body contours in contact with said pad; and b. a thin-filmenvelope inclosing said gel.